Printrbot Jr. saves the day

Well, I’ve had the Printrbot Jr. up and running for over a month now. Maybe more. Had plenty of help putting it together. The design is quite nice and appears to be well thought out. The kids had little trouble following along and putting the pieces together.

The instructions at the time consisted only of a youtube video but was decent enough to figure out where it all went. The only catch was a belt threaded through differently than the firmware expected but that was easy to sort out after the fact by swapping a few wires on the stepper connector.

I spent a bunch of time figuring out how to run the wires and make it all pretty. The wires all come with connectors on them ready to plug in but that leads to a bit of a bundle of wires to jam into the small electronics compartment. I cut all the wires to length and replaced the connectors. That resulted in a much less busy enclosure and might aid in cooling hopefully.

I’ve been having troubles getting the PLA to stick to my blue 3M tape bed. As the PLA squirts from the nozzle, it just didn’t appear to stick well and tended to curve up with the nozzle. I tried different print heights and speeds. With a little patience it was possible to get a smaller print done. Quality is pretty nice once the first layer sticks down.

The PLA has more trouble with overhangs than I’m used to with ABS. I tried printing a Pikachu that I’ve done before with ABS. The model has two small hands which overhang out the front. With ABS the first layer was ugly but the next one worked nicely and the print was beautiful. The PLA had much more trouble. I can see that a fan will come in very handy.

This past weekend I did a bit of poking around and discovered that the plywood bed is curved across itself diagonally so all my efforts to level the bed at the corners had been wasted mostly. The center where I do the printing was raised so all the PLA was getting smooshed in that area. If I dropped the bed a bit to accommodate it, then anything not at the center of the bed wouldn’t stick very well.

So I took the bed off and flipped it over so it curved downwards instead. I then cut a piece of glass to the right size and clipped it on the bed. That gave a nice flat surface to print on.

It didn’t help my sticking issue though. Apparently I was fighting 2 battles and hadn’t known it. I decided that I likely needed to build a small heated bed for the Printrbot Jr. before pushing it into heavier use. I put that onto the list of things to do and went back to my Prusa for the what I figured was the time being.

I needed to print out a bunch of glow in the dark Minecraft Creepers which required my ABS anyhow. After about 3 hours of printing I started getting jams. I blamed crud in the filament given that I’ve been using cheap stuff and forged ahead. The problem kept recurring. I ran out of time that night and came back to it the next day. Started printing again and all is good. Then about 2 or 3 hours in, the jamming starts again. I tweaked settings, played with various things and no luck. And then it happened…. total jam. Couldn’t even force the filament through by hand. Uh oh… more serious.

I’ve been using an Arcol V3 hotend for a long while now and have been pretty happy with it. Its a bit of a pain to disassemble though. Its an early version and doesn’t haven’t any of the nicer features like flats on the nozzle to help pull it apart.

So I pulled the nozzle off my printer and set about pull it it all apart to get whatever was jamming it out. Everything came apart pretty nicely aside from the nozzle from the heater block body. I found a gap between the nozzle and the PTFE tube where ABS had been collecting. There was also some scorching on the Peek where it screws into the nozzle. It looked like a small bit of ABS material might have started to squeezed out these threads. Likely from all the pressure caused by the plug.

I heated up the extruder and set about trying to separate the nozzle and heater block. It unscrewed about half way and then jammed. Couldn’t go forward, couldn’t go back. A more patient person would have let the whole thing just sit in acetone for the night to see if that loosened things up. I on the other hand pulled out the vice grip and started twisting. All that accomplished was jamming it a little bit more and then turning the round nozzle body into an oval. No chance of getting a nice seal with the peek portion every again.

So… two choices at this point. Reorder another nozzle from Arcol, wait 3 weeks or so reassemble and hope that the gap between the PTFE and peek doesn’t cause any issues later, or go to a different hot-end design. I love change so I started looking at new hotends. 😉 The Arcol V4 looks awesome but is pricey. Eckertech has a cool looking hotend. I’ve been using their hobbed bolt, their Prusa V1 plastics and their 3mm filament for some things and I know they are a quality operation. The only catch was the active cooling requirement and the fan that would hang off the side. It meant replacing my carriage, running more power down there and finding room for the fan.

In the end, I went with the J-Head Mk V from Reifsnyder Precision Works. The version 4 has been used quite a bit by others and has a good reputation. The version 5 is more of the same but smaller and tweaks. Who could resist. I’ve been looking for an excuse to try it out. Of course, the catch is that they are out of stock at Hot-ends and it would have taken a few weeks anyhow.

Voxel Factory to the rescue! I’ve had my eye on them for a while. The filament prices are pretty good, especially if I was in Montreal and could just pick it up. They have good prices on electronics and other goodies too. And they have the hot ends that I need. Or so I hope… they don’t display stock levels on their website. I ordered two of them so I’m hoping that they ship out today and I’ll have them next week. Fingers crossed. [update from comments below… in stock and shipped today!]

So, how does the Printrbot save the day? Well, my extruder body is custom printed just for the Arcol head. It has a different mounting system than a normal hot-end. I’ve also done some tweaking on the extruder itself also to squeeze the stepper motor closer and give me a little extra room on my X axis. So I needed a new extruder printed which would have the j-head mount. Piece of cake… fired up OpenSCAD, added a hole and screw mounts for the j-head and dumped out a new STL.

Now to sort out the print problems with the Jr. Tried slowing the first layer down to 5mm/s and then 3mm/s. Sticks better but not good enough. Tried with a raft. No good. I finally remembered that some people were using hair spray or sugar water to make it stick. No hair spray around but sugar water was easy to mix up. I dabbed it on the 3M tape and then hit it with the heat gun to dry up the water and leave behind the stickiness. Then it occurred to me… just use the heat gun and get the bed warm for the first layer.

So I did. Well… sugar water, heat-gun and raft all to make sure it worked. Stuck down like a charm. The raft wasn’t necessary as it turned out. I’m not convinced that the sugar water did much either. I think it was all heat gun awesomeness.

So, new extruder body ready to go. Just need to get the new hot-end and I’m back in action. Handy to have a spare printer when one printer goes down!

Now to start laying out a custom heated PCB bed for the Printrbot Jr. Looks like it will save me some trouble later on!

That is great news! I saw your post on the Reprap forums about the nylon but I didn’t have filament on my mind when I was making the hotend order. I’ll have to put together a PLA + Nylon order in the new year once I get my Prusa back up and running.

I see that you have some experience and success in printing in 3D (I like the models!), and also that you have built/used a Prusa Mendel.

I am an engineer currently in Ottawa and was wanting to get into 3D printing myself by building/operating a Prusa Mendel. I was wondering if I could meet/contact you at some point in the near future to discuss your experiences with the Mendel and what it is you do to get such good quality prints.

I see that the robotics club meets up at Algonquin College ( I currently study business there!) so maybe I can meet you before, after, or during a meeting at AC?

Absolutely. There are a bunch of little mechanical things to sort out initially with these 3D printers and then it is pretty clear sailing. I’m happy to give any hints and suggestions that I can to get you past that.

The next Ottawa robotics meeting is January 14th and I can be sure to bring both of my printers to demonstrate.

I’m using 3mm filament with a 0.5mm nozzle (default that came with the Jr back when I bought it). I’m using KissSlicer primarily for the slicing and Repetier for the printing. I spend a bit of time printing test prints which each filament roll I have and do some tuning. Typically that just means setting the correct diameter for it (averaging what variation I see) and then adjusting the flow rate if I find that I need to tweak it (increase flow rate if I need more material, decrease if I need left). I’ve found that PLA needs anywhere from 5 to 10% extra flow to get nice performance with KissSlicer and I’ve been using a 60% overlap between infill and perimeter instead of the default 50%.

The default steps/mm settings that come with the Printbot Jr for the extruder (programmed in the EEPROM) were way way out on my printer. I don’t know if that is true any more or not, but it is definitely something that you want to measure. Mark off 10cm on your filament and run it through the printer. Increase/decrease the extruder steps/mm to match.

And definitely put glass + painters tape on your bed. A little rub with acetone (picked up from your local hardware store) on fresh tape and it will stick nicely (assuming you are using PLA). Getting the bed flat was a huge improvement for me.